I'll chip in on this with my opinion on the matter, I guess:
(I will note beforehand that I'm biased against buying an instrument new; as I don't think it's very economical compared to buying one used and having it overhauled by a good repairman.)
I started out on an instrument that most definitely wasn't new; and I know a lot of other people have also, and that doesn't seem to be holding them back if it's in good shape.
However the most important thing is that it's both a good instrument and in good playing shape; of which being new does encourage the second, typically. (My mom had the Selmer Signet I started on that she used to play in elementary school repadded before I started band, for example of the being in good shape.)
Also, +∞ for having a good teacher; both for playing it to make sure its in good shape; and for making sure you're doing everything correctly; that's very important, imho.
(I'll add in case that doesn't show up on some browsers/operating systems that should be an infinity symbol after the plus.)